As a reference shot, I removed these rings from a Campy NR crank on a used bike I bought in 1977. I swapped the rings partly because they are well worn and partly because I wanted to go back to Campy rings. I always assumed these were factory drilled by Sugino, I could be wrong. The small holes are chamfered on both sides. In any case a set such as these could be used as pilots for a DIY pattern for rings of the same size, using chain ring bolts to attach the pattern to the subject ring. The pattern could be varied by drilling different hole sizes in different locations if a center drill is first employed.